D-mannitol is a six-carbon sugar alcohol or polyol, which is about half as sweet as sucrose and occurs widely in nature in a variety of organisms including plants, algae, fungi, and certain bacteria. L-mannitol does not occur naturally.
Low levels of mannitol are found in several fruits and vegetables. Presently, mannitol is industrially produced by catalytic hydrogenation of fructose/glucose (1:1) mixture such as invert sugar. Raney-nickel is used as a catalyst and hydrogen gas is used at high temperature and pressure (Makkee et al., 1985). The disadvantage of this method is that the composition of the hydrogenated mixture consists of only about 25% mannitol and the remaining 75% was sorbitol. This production procedure makes the manufacture cost for mannitol relatively high.
Mannitol is known to have several applications both in plants and humans. Jennings (1984) stated that polyols including mannitol play several roles in fungi; as carbohydrate reserve, as translocatory compounds, as an osmoregulatory compound as in coenzyme regulation, storage or reducing power and has been also shown to quench reactive oxygen species (ROS). Reactive oxygen species are both signal molecules and direct participants in plant defense against pathogens. There is growing evidence that at least some phytopathogenic fungi use mannitol to suppress ROS mediated plant defenses (Jennings et al 1998).
Mannitol is a valuable nutritive sweetener because it is non-toxic, non-hygroscopic in its crystalline form and has no teeth decaying effects (Debord et al 1987; Dwivedi 1978). Mannitol does not induce hyperglycemia, which makes it useful for diabetics (Griffin and Lynch, 1972). It is used as a sweet builder in sugar free chewing gum and in pharmaceutical preparations (Soetaert, 1991).
The other uses of mannitol are that it is used for the treatment of ciguatera in Australia (Lewis, 1992). In emergency cases, mannitol is used in the treatment of head injury to decrease cerebral edema and intracranial pressure. Administration of mannitol in man induces diuresis (promotion of urinary excretion) in oligourea or forced diuresis in food poisoning cases. High doses of mannitol exert a laxative effect in man.
Several microorganisms are known to produce mannitol. Among bacteria, heterofermentative species belonging to the genera Leuconostoc, Oenococcus, and Lactobacillus seem to be most effective in producing mannitol (Niklas et al 2002). Several filamentous fungi (moulds) produce mannitol form glucose as well. Mannitol was earlier reported from fungal strains like Aspergillus niger (Muraleedharan, 1988), cotton dust associated fungi viz. Alternaria alternata, Cladosporium herbarum, Epicoccum purpurascens and Fusarium pallidoroseum (Domelsmith et al 1988), Candida magnoliae (Song et al 2002) and Cephalosporium sp. (Bi et al 2001).
The prior art biotechnical process for the conversion of sugar to mannitol has not proven entirely satisfactory, as they do not provide an adequate conversion yield and therefore the industrial production is still based on hydrogenation. Thus, there remains a need to improve the bioconversion of fructose and other substrate into mannitol in order to provide an industrially economical and acceptable process.
Our fungal culture, NIO-FM1E#001 shows a considerable good yield (˜70% of the total crude extract) and a relatively simple and economical process for the production of mannitol. Since mannitol has been reported to accumulate in response to environmental stress (Kets et al 1996; Stoop and Pharr, 1994), the fungus, NIO-FM1E #001 was cultured under thermal and salt stress conditions to obtain maximum yield of polyol. Thus, our patent describes an economical process for the production of mannitol and a novel fungal source (NIO-FM1E#001) for the production of the same.